Sin (420⁰) cos (390⁰) +cos (-300⁰) sin (-330⁰) = -1
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Answer:
Step-by-step explanation:
Sin (420°) cos (390°) + cos (-300°) sin (-330°)
= sin (360°+60°) cos (360°+30°) + cos (300°) -sin (330°)
= sin (360°+60°) cos (360°+30°) - cos (360°-60°) sin (360°-30°)
= sin 60° cos 30° - cos 60° (-sin30°)
= root 3/2 × root 3/2 + 1/2 × 1/2
= 3/2 + 1/4
= 6+1/4
= 7/4 is the answer
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